The invention relates to a seal for use in an extrusion device for producing continuous profiles, in particular plastics pipes.
Seals of this type are known in a variety of embodiments. An established sealing principle is applied for example in pipe extrusion systems with a changeable pipe diameter in operation at the outlet of the vacuum chamber, between the vacuum chamber and the downstream water tank in the extrusion direction. The so-called segment seal comprises radially movable segments arranged around the pipe and in extrusion direction before the segment arrangement a simple elastic sealing disc with a passage opening for the extruded pipe. This functions because the flow direction (also sealing direction or pressure drop direction) acts contrary to the extrusion direction owing to the negative pressure in the vacuum tank. However, this principle can not be readily transferred to other regions of the extrusion system, as soon as the sealing direction and the extrusion direction are aligned. The sealing disc is then destroyed, because for example it remains adhered to the pipe or is drawn into the segment arrangement.
For example in extrusion direction behind the water tank, where the extrusion direction and the sealing direction are aligned, therefore frequently funnel seals have been used. These are indeed not destroyed, but are only at all practicable with very small diameters (approx. up to 250 mm) (the pressure build-up by the water is too great in the case of large diameters, so that a sealing action is no longer achieved) and have the disadvantage, within the region which is changeable in diameter, of the deficient sealing action in the case of smaller pipe diameters or so-called chattering in the case of larger diameters. Furthermore, such seals are subject to a large amount of wear, should therefore be easily replacable and advantageously have a lower cost for materials.